Automotive Electronics for Mechanical Engineering

SYLLABUS
UNIT IV: VEHICLE MOTION CONTROL AND AUTOMOTIVE
DIAGNOSTICS
Cruise control system, Digital cruise control, Timing light, Engine
analyzer, On-board and off-board diagnostics, Expert systems.
Stepper motor based actuator, Cruise control electronics,
Vacuum – antilock braking system,Electronic suspension system
Electronic steering control, Computer-based instrumentation
system, Sampling and Input and output signal conversion, Fuel
quantity measurement, Coolant temperature measurement, Oil
pressure measurement, Vehicle speed measurement, Display
devices, Trip-Information- Computer

Cruise Control System
What is cruise control system
The purpose of a cruise control system is to accurately
maintain a speed set by the driver without any outside
intervention by controlling the throttle-accelerator pedal
linkage.
The earliest variants of cruise control were actually in use
even before the creation of automobiles.
The inventor and mechanical engineer James Watt developed
a version
as early as the 17th century, which allowed steam engines to
maintain a constant speed up and down inclines.
Cruise control as we know it today was invented in the late
1940s, when
the idea of using an electrically-controlled device that could
manipulate road speeds and adjust the throttle accordingly was
conceived.

Cruise Control System
How does cruise control work?
The cruise control system controls the speed of your car the
same way you do – by adjusting the throttle (accelerator)
position.
However, cruise control engages the throttle valve by a cable
connected to an actuator, rather than by pressing a pedal.
The throttle valve controls the power and speed of the engine
by
limiting how much air it takes in (since it’s an internal
combustion engine).
The driver can set the cruise control with the cruise
switches, which
usually consist of ON, OFF, RESUME, SET/ACCEL and COAST.
These are commonly located on the steering wheel or on the
windshield wiper or turn signal stalk.
The SET/ACCEL knob sets the speed of the car. One tap will
accelerate it by 30km/hr mph, two by 31km/hr and so on.
Tapping the knob in the opposite direction will decelerate the
vehicle. As a safety feature, the cruise control system will

Cruise Control
System
Figure: Block Diagram of Cruise Control
System

Adaptive Cruise Control System
Adaptive cruise control (ACC) is an active safety system
that automatically controls the acceleration and braking
of a vehicle.
It is activated through a button on the steering wheel and
cancelled by driver’s braking and/or another button.
Figure: Adaptive Cruise
Control

Adaptive Cruise Control
How does adaptive cruise control work?
By monitoring other vehicles and objects on the road,
adaptive cruise control enables a safe and comfortable
driving experience.
It does so by helping the driver keep a steady vehicle speed at
a given moment.
The driver can set their preference regarding certain factors,
such as
the distance to the car in front, driving mode – for
example, economical, sporty or comfortable – and
others.
Together with information about speed limits, road
curvature,
accidents data and more, these choices influence the
automatically selected speed.
Cruise control has come a long way from its early days in
its quest to
assist drivers on the road.
When first introduced, it was only found in luxury car models

Adaptive Cruise
Control
Figure: Block Diagram:- Adaptive Cruise Control
System

Automotive Electronics for Mechanical Engineering

On-Board Vs Off-Board Diagnosis
The state of the motion or rest of the car becomes
primarily important.
Also, the diagnostics parameters change when the vehicle
is moving and when it is at rest in a garage.
In order to cover both these scenarios, off-board and on-
board vehicle diagnostics have been introduced.
The typical vehicle diagnostics feature checks the state of
functions performed by the subsystems, sensors and other
such components.
The errors reported by all these components are recorded in
the error memory in the form of DTCs (Diagnostic Trouble
Codes).
While on-board vehicle diagnostics protocols like OBD/OBD2
are tasked primarily with emission related diagnosis, off-
board vehicle diagnostics (UDS, KWP etc.) handle the
diagnostics related to every other vehicle ECU (Electronic

On-Board Vs Off-Board Diagnostics
What’s the Functional Scope of On-board Diagnostics System
On-board vehicle diagnostics (OBD2) comes into the picture
when the vehicle is moving.
The tests are being conducted while the vehicle is on the road.
The test results can be seen on the vehicle’s dashboard in the
form of MIL (Malfunction indicator light) or an OBD tester tool.
The data that the OBD makes accessible is related to:
Emission Control System
Engine and Transmission ECUs (powertrain)
OBD2 was mandatory for all the cars that were
manufactured in the USA after the year 1996.
This was essentially done to keep the emissions level of the
vehicles in check.
Every parameter related to the vehicle emission such as info
from
oxygen sensors and the fuel injectors etc. is checked.
In case of any malfunction, an MIL (malfunction indicator
light) is triggered to warn the vehicle owner.

The error that triggers the MIL is also stored in the
automotive ECU which can later be retrieved by the tester
tool at the garage.
This error code helps the technicians to pin-point the
emission issue and rectify it.
The technician sends the PIDs and gets the response
corresponding to
that PID.
The technician can then zero in on the specific issue that is
causing the trouble.
These tester tools perform generic tests that are similar for
most
vehicles.

What’s the Functional Scope of Off-board Diagnostics
System
Off-board vehicle diagnostics takes care of the diagnostics
of every other vehicle ECU function other than emission.
There are several protocol standards defined for off-board
diagnostics, however, Unified Diagnostics Services (UDS) is the
most popular diagnostic protocol.
The diagnostics manager of the UDS protocol stores every issue as
fault
codes called Diagnostics Trouble Code (DTC).
When a vehicle is running, the off-board diagnostics is also active.
However, the contrast with on-board diagnostics lies in the
reporting part.

In case of OBD, the fault is communicated to the information
cluster by triggering the Malfunction indicator light.
Whereas, in the off-board diagnostics, no such instant
reporting is carried out.
The issue is stored in the EEPROM part of the vehicle ECU
for
retrieval at the service garage using a vehicle diagnostic testing
tool.
The scope of off-board diagnostics (UDS) is not limited to just
storing the diagnostic trouble codes (DTCs).
It is capable of offering services such as vehicle ECU
reprogramming,
remote routine activation, writing data on the automotive
Electronic Control Unit and even more.

Modern Automotive Instrumentation
The evolution of instrumentation in automobiles has been
influenced by electronic technological advances in much the
same way as the engine control system.
Of particular importance has been the advent of the
microprocessor,solid-state display devices, and solid-state
sensors.
Figure: General Instrumentation
System

In electronic instrumentation, a sensor is required to
convert any nonelectrical signal to an equivalent voltage
or current.
Electronic signal processing is then performed on the sensor
output to produce an electrical signal that is capable of
driving the display device.
The display device is read by the vehicle driver.
If a quantity to be measured is already in electrical form (e.g.
the battery charging current), then this signal can be used
directly and no sensor is required.
In contemporary automotive instrumentation, a
microcomputer (or related digital subsystem) performs all
signal-processing operations for several measurements.
The primary motivation for computer-based
instrumentation is the great flexibility offered in the
design of the instrument panel.

Modern Automotive
Instrumentation
Figure: Computer Based Instrumentation
System

All measurements from the various sensors and switches are
processed in a special-purpose digital computer, i.e. the
instrumentation computer.
The processed signals are routed to the appropriate display
or warning message.
It is common practice in modern automotive
instrumentation to integrate the display or warning in a
single module that may include both solid-state
alphanumeric display, lamps for illuminating specific
messages, and traditional electromechanical indicators.
For convenience, this display system will be termed the
instrument panel (IP).

The inputs to the instrumentation computer include
sensors (or switches) for measuring (or sensing) various
vehicle variables as well as diagnostic inputs from the other
critical electronic subsystems.
The vehicle status sensors may include any of the following:
1
2
3
4
5
6
7
8
9
fuel quantity
fuel pump
pressure fuel
flow rate vehicle
speed
oil pressure
oil quantity
coolant
temperature
outside ambient
temperature windshield
washer fluid quantity
10 brake fluid
quantity

The input may include switches for determining gear selector
position, brake activation, and detecting open doors and
trunk, as well as IP selection switches for multifunction
displays that permit the driver to select from various display
modes or measurement units.
Modern instrumentation systems is to receive diagnostic
information from certain subsystems and to display
appropriate warning messages to the driver.
The powertrain control system, for example, continuously
performs self-diagnosis operation.
If a problem has been detected, a fault code is set
indicating the nature and location of the fault.
This code is transmitted to the instrumentation
system via a powertrain digital data line (PDDL).
This code is interpreted in the instrumentation
computer and a “Check Engine” warning message is
displayed.

Input-Output Signal Conversion
A typical instrumentation computer is an integrated
subsystem that is designed to accept all of these input
formats.
A typical system is designed with a separate input from each
sensor or switch.
An example of an analog input is the fuel quantity sensor,
which can be a potentiometer attached to a float
Figure: Digital Instrumentation
System

What is ADC?
ADC (Analog to Digital Converter) is an electronic device that
converts a continuous analog input signal to discrete digital
numbers.
Analog
Real world signals that contain noise
Continuous in time
Digital
Discrete in time and value
Binary digits that contain values 0 or 1

Why is ADC Important?
☐ All microcontrollers store information using digital logic
Compress information to digital form for efficient storage
Medium for storing digital data is more robust
Digital data transfer is more efficient
Digital data is easily reproducible
Provides a link between real-world
signals and data storage
☐
☐
☐
☐
☐

How ADC Works
2 Stages:
☐ Sampling
Sample-Hold Circuit
Aliasing
☐ Quantizing and Encoding
Resolution
Binary
output

Sampling
☐ Reduction of a continuous signal to a discrete signal
Achieved through sampling and holding circuit
Switch ON – sampling of signal (time to charge
capacitor w/ Vin)
Switch OFF - voltage stored in capacitor (hold operation)
Must hold sampled value constant for digital conversion
☐
☐
☐
☐
Response of Sample and Hold Circuit
Simple Sample and Hold Circuit

Sampling
☐ Sampling rate depends on clock
frequency
Use Nyquist Criterion
Increasing sampling rate
increases accuracy of
conversion
Possibility of aliasing
☐
☐
☐
fs
Ts 
1
Sampling Period:
Nyquist Criterion: fs  2  f max
Sampling Signal: Tw

Aliasing
☐ High and low frequency samples are indistinguishable
Results in improper conversion of the input signal
Usually exists when Nyquist Criterion is violated
Can exist even when: fs  2  f max
Prevented through the use of Low-Pass (Anti-
aliasing) Filters
☐
☐
☐
☐

Quantizing and Encoding
☐ Approximates a continuous range of values and
replaces it with a binary number
Error is introduced between input voltage and output
binary representation
Error depends on the resolution of the ADC
☐
☐

Resolution
resolution  Vrange /(2n
1)
Example:
Vrange 
7.0V n  3
1V  7V
/(23
1)
Vrange=Input Voltage Range
n= # bits of ADC
Resolution
Qerror  resolution /
2
 .5V

Resolution
☐ Increase in resolution improves the accuracy of the
conversion
Minimum voltage step recognized by ADC
Analog Signal Digitized Signal- High
Resolution
Digitized Signal- Low
Resolution

Flash A/D Converter
Successive Approximation A/D
Converter Example of Successive
Approximation Dual Slope A/D
Converter
Delta – Sigma A/D Converter
Types of A/D
Converters

FLASH A/D CONVERTER
3 Bit Digital
Output
Resolution
23-1 = 7
Comparators

What is a DAC?
DAC
100101
…
A digital-to-analog converter (DAC) takes a digital code
as its input and produces an analog voltage or current
as its output. This analog output is proportional to the
digital input.

Digital to Analog Conversion (DAC)
 Digital to Analog conversion involves
transforming the computer’s binary output in
0’s and 1’s (1’s typically = 5.0 volts) into an
analog representation of the binary data
 DAC:
 n digital inputs for digital
encoding
 analog input for Vmax
 analog output a
DAC
Vmax
x0
x1
Xn-1
…
a
 General Concept:

 Applications for Digital to Analog Converters:
 Voltage controlled Amplifier
digital input, External Reference
Voltage as control
 Digitally operated attenuator
External Reference Voltage as input,
digital control
Circuit Components

 Applications for Digital to Analog Converters:
Motor Controllers
 Cruise
Control
 Valve
Control
 Motor
Control

Types of DAC
 Many types of DACs available
– Binary Weighted Resistor
– R-2R Ladder
– Multiplier DAC
– Non-Multiplier DAC
• Among them Weighted & R-2R are commonly used.

Digital to Analog Converter(DAC)
Utilizes A Inverting
Weighted Op-amp
Circuit.
Weighted Resistors Are
Used To Distinguish Each
Bit From The Most
Significant To The Least
Significant
Binary Weighted Resistor
Rf
2
R
R
V
o
-VREF
 i
I
LSB
4
R
8
R
MS
B
General Concept:

 Binary Representation
VREF
Least
Significant Bit
Most
Significant Bit
CLEARED
SET
( 1 1 1 1 )2 = ( 15 )10
Binary Weighted Resistor














R
V
R
V
R
V
R
V
R
IR
V
8
4
2
4
3
2
1
f
f
out
MSB
LSB
LSB
MS
B
V
K
K
K
K
K
K
K
K
V 13
1
10
10
0
5
10
1
5
.
2
10
1
25
.
1
10
out 
















Output Voltage Analysis

The analog inputs must all be converted to digital format
using an analog-to-digital (A/D) converter
a quantity x being measured uses an analog sensor
with output voltage V0(x ) .
The instrumentation computer causes a sample of V0 to be
taken at time tk via a sample and hold(SH) circuit.
The sampled voltage vo (tk ) is, then, converted to a digital
input vk
by the A/D converter and is input to the CPU in digital
format.
The digital inputs are already in the desired format.
The conversion process requires an amount of time that
depends primarily on the A/D converter.
After the conversion is complete, the digital output
generated by the A/D converter is the closest possible
approximation to the equivalent analog voltage, using an M-

The A/D converter then sends a signal to the computer by
changing the logic state on a separate lead (labeled
EOC,indicating end of conversion) that is connected to the
computer.
The output voltage of each analog sensor for which the
computer performs signal processing must be converted
in this way.
Once the conversion and any required digital signal
processing are complete, the digital output is transferred
to a register in the computer.
If the output is to drive a digital display, this output can
be used directly.
However, if an analog display is used, the binary number
must be converted to the appropriate analog signal by using
a digital-to-analog (D/A) converter.

Input-Output Signal
Conversion
A typical D/A converter used to transform digital computer
output to an analog signal is shown below
]
Figure: Digital Input Analog
Output

Input-Output Conversion
The N digital output leads transfer the results of the signal
processing to a D/A converter.
When the transfer is complete, the computer sends a
signal to the D/A converter to start converting.
The D/A output generates a voltage that is proportional to
the binary number in the computer output.
The D/A conversion often includes a zero-order hold circuit
(ZOH).
A low-pass filter (which could be as simple as a capacitor)
is often connected across the D/A output to smooth the
analog output between samples.
The sampling of the sensor output, A/D conversion, digital
signal processing, and D/A conversion normally take place
during the time slot allotted for the measurement of the
variable in a sampling time sequence (although time delays
are possible)

Advantages of Computer Based
Instrumentation
One of the major advantages of computer-based
instrumentation is its great flexibility.
To change from the instrumentation for one vehicle or one
model to another often requires only a change of computer
program.
This change can often be implemented by replacing one
ROM with another.
The program is permanently stored in a ROM that is
typically packaged in a single integrated circuit
package.
Another benefit of microcomputer-based electronic
automotive instrumentation is its improved
performance compared with conventional
instrumentation.

Advantages of Computer Based
Instrumentation
The traditional electro-mechanical fuel gauge system has
errors that are associated with
1 Nonlinearities in the mechanical and geometrical
characteristics of the tank relative to the sender unit
The instrument voltage
regulator The display
dynamic response
2
3
The electronic instrumentation system eliminates the
error that results from imperfect voltage regulation.
In general, the electronic fuel quantity measurement
maintains calibration over essentially the entire range of
automotive operating conditions.
It significantly improves the display accuracy by replacing
the
electro-mechanical galvanometer display with an all-
electronic digital display.

Fuel Quantity Measurement
During a measurement of fuel quantity, the MUX switch
functionally connects the computer input to the fuel
quantity sensor.
This sensor output is converted to digital format and then
sent to the computer for signal processing.
Figure: Fuel Quantity Management
System

Fuel Quantity
Measurement
Figure: Fuel Quantity Sensor
Configuration

A potentiometer was introduced as a sensor for
measuring throttle angular position.
It also has application in certain fuel-measuring
instrumentation.
A constant current passes through the sensor
potentiometer, since it is connected directly across the
regulated voltage source.
The potentiometer is used as a voltage divider so that the
voltage at the wiper arm is related to the float position,
which is determined by fuel level.

The sensor output voltage is not directly proportional to fuel
quantity in gallons because of the complex shape of the fuel
tank.
The computer memory contains the functional relationship
between sensor voltage and fuel quantity for the particular
fuel tank used on the vehicle.
The computer reads the binary number from the A/D
converter that corresponds to sensor voltage and uses it to
address a particular memory location.
Another binary number corresponding to the actual fuel
quantity in gallons for that sensor voltage is stored in that
memory location.
The computer then uses the number from memory to
generate the appropriate display signal (either analog or
digital, depending on display type) and sends that signal
via DEMUX to the display.

Coolant Temperature Measurement
The measurement of this quantity is different from that of
fuel quantity because usually it is not important for the driver
to know the actual temperature at all times.
For safe operation of the engine, the driver only needs to
know that the coolant temperature is less than a critical
value.
The coolant temperature sensor used in most cars is a
solid-state sensor called a thermistor.
Where it was shown that the resistance of this sensor
decreases with increasing temperature.

Coolant Temperature
Measurement
Figure: Coolant Temperature Measurement
System

Coolant Temperature
Measurement
Figure: Coolant Temperature Sensor
Unit

Coolant Temperature Measurement
The sensor output voltage is sampled during the appropriate
time slot and is sampled (S) converted to a binary number
equivalent by the A/D converter.
The computer compares this binary number to the one
stored in memory that corresponds to the high-
temperature limit.
If the coolant temperature exceeds the limit, an output
signal is generated that activates the warning indicator.
If the limit is not exceeded, the output signal is not
generated and the warning message is not activated.
A proportional display of actual temperature can be
used if the memory contains a cross-reference table
between sensor output voltage and the corresponding
temperature.

Automotive Electronics for Mechanical Engineering

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